It is important to suppress the power consumption in a small liquid crystal display used in a cellular phone or the like. In a liquid crystal display, a liquid crystal screen whose light transmissivity is controllable is illuminated with a backlight from the back and an image is displayed with a transmitted light. Since most of the power in the liquid crystal display is consumed by the backlight, it is very effective to suppress the power consumption of the backlight for reducing the power consumption of the liquid crystal display.
For its achievement, Japanese Patent Application Laid-Open Publication No. 11-65531 has proposed a method, in which the maximum value of the grayscale of a display image: x is acquired, the data of the entire image is extended so that the maximum value of the grayscale of the display image: x becomes the maximum grayscale of the liquid crystal display screen (255 grayscale in 8-bit RGB), and the light amount of the backlight is lowered so that a luminance value in the maximum grayscale (255 grayscale) becomes the luminance value of the maximum value of the grayscale of the display image, thereby reducing the power consumption.
Further, in order to reduce the power consumption, Japanese Patent Application Laid-Open Publication No. 11-65531 provides a method, in which a histogram of the grayscale of a display image is acquired, image data is extended with using a grayscale value P1, at which a cumulative value of the histogram from the maximum grayscale of the display image is equivalent to the predetermined number of pixels, as the maximum grayscale, and the light amount of the backlight is lowered so that the luminance value in the maximum grayscale (255 grayscale) display becomes the luminance value of the grayscale value P1, thereby reducing the power consumption.